This application is based on Japanese patent application JP 2004-209902, filed on Jul. 16, 2004, the entire content of which is hereby incorporated by reference, the same as if set forth at length.
1. Field of the Invention
The present invention relates to a functional device and a method for the production thereof and a solid-state image pickup device and a method for the production thereof and more particularly to a photoelectric conversion element comprising a photoelectric conversion layer containing an organic material and a light-transmitting electrode stacked on the photoelectric conversion layer and a solid-state image pickup device comprising such a photoelectric conversion element and a method for the production thereof.
2. Description of the Related Art
A prototype device of a photoelectric conversion layer stacked type solid-state image pickup device is, for example, one described in JP-A-58-103165. This solid-state image pickup device is constructed such that three layers of photosensitive layers are stacked on a semiconductor substrate; and respective red (R), green (G) and blue (B) electric signals as detected in the respective photosensitive layers are read out by a MOS circuit formed on the surface of the semiconductor substrate.
Though the solid-state image pickup device having such a construction was proposed in the past, a CCD type image sensor and a CMOS type image sensor in which a number of light receiving parts (photodiodes) are integrated in a surface portion of a semiconductor substrate and respective red (R), green (G) and blue (B) color filters are stacked on the respective light receiving parts have extremely progressed. At present, an image sensor having several millions light receiving parts (pixels) integrated on one chip has been mounted in a digital still camera.
However, with respect to the CCD type image sensor or CMOS type image sensor, the technical progress reaches the vicinity to limits, and the size of the light receiving region (opening) of one light receiving part is about 2 μm and becomes closed to the order of a wavelength of incident light, resulting in facing a problem that the production yield is poor.
Further, an upper limit of the quantity of photoelectric charges to be accumulated in one miniaturized light receiving part is low as about 3,000 in terms of the number of electrons, so that it becomes difficult to express 256 gradations. For this reason, it is difficult to expect to realize more properties in the image quality and sensitivity by the related art CCD type or CMOS type image sensors.
Then, as a solid-state image pickup device for solving these problems, the structure of the solid-state image pickup device as proposed in JP-A-58-103165 is given a second look, and image sensors as described in Japanese Patent No. 3,405,099 and JP-A-2002-83946 are newly proposed.
The image sensor as described in Japanese Patent No. 3,405,099 is constructed such that an ultra-fine particle of silicon is dispersed in a medium to form a photoelectric conversion layer; three layers of plural photoelectric conversion layers having a varied particle size of the ultra-fine particle are stacked on a semiconductor substrate; and electric signals are generated in the respective photoelectric conversion layers corresponding to the respective light receiving quantities of red, green and blue colors.
This applies also to the image sensor disclosed in JP-A-2002-83946. This image sensor comprises three nanosilicon layers composed of particles having different particle diameters stacked on a semiconductor substrate. This image sensor is arranged such that red, green and blue electric signals detected by the respective nanosilicon layer are read out by storage diodes formed on the surface of the semiconductor substrate.
In order to stack a photoelectric conversion layer having such a configuration on a semiconductor substrate, two light-transmitting electrodes are stacked with the respective photoelectric conversion layer provided interposed therebetween. This light-transmitting electrode may need to be patterned as necessary. As ordinary methods of patterning a light-transmitting electrode there have been proposed methods disclosed in JP-A-2000-150466 and JP-A-2000-150467.
For the sake of putting a photoelectric conversion layer stacked type solid-state image pickup device into practical use, it is necessary to solve a problem on what materials are to be used for forming a photoelectric conversion layer. In the related art technologies as described in Japanese Patent No. 3,405,099 and JP-A-2002-83946, the photoelectric conversion layer is made of an ultra-fine particle of silicon or constructed of a nano-silicon layer. However, more actually, it may be said to be preferable that the photoelectric conversion layer is made of an existing material, for example, an organic material such as organic semiconductors.
However, there arises a problem that when a photoelectric conversion layer containing an organic material and a light-transmitting electrode are stacked on a semiconductor substrate and the light-transmitting electrode is then subjected to patterning according to the method disclosed in JP-A-2000-150466 and JP-A-2000-150467, the resulting photoelectric conversion layer exhibits deteriorated photoelectric conversion characteristics, making it impossible to take images having a high resolution.